LONDON (Reuters) - Queen Elizabeths 60 years on the British throne will be celebrated next year with four days of events including a flotilla on the River Thames and a concert at Buckingham Palace, royal officials said on Thursday. The 85-year-old, who last month became the second-longest reigning British monarch in more than 1,000 years, acceded to the throne on the death of her father George VI on Feb. 6, 1952. She will overtake Queen Victoria, who ruled for much of the 19th century, to become the longest reigning monarch in September 2015. Festivities to mark the diamond jubilee will begin on Saturday, June 2 when the monarch will attend the Epsom Derby horse race. The following day will see the Big Jubilee Lunch when people will be encouraged to get together with their neighbours and friends to share a meal, possibly at street parties or picnics. On the same day, up to 1,000 boats will also assemble on the Thames in London for the biggest flotilla seen in modern times with the queen at the head in the royal barge.